Optical information recording condition adjustment method, recording/reproducing method and apparatus

ABSTRACT

The recording strategy is optimized by determining a pulse response so as to minimize the difference between the reproduced waveform obtained by recording and reproducing the recording pulse signal wherein the record data is superposed with a high-frequency pulse and the waveform calculated by convolution of the record data and pulse responses. In this process, a single recording pulse waveform is recorded on a single track of the optical recording medium for three or more times, and sampled values z p,1 , . . . , z p+3,1 , . . . , . . . , z p,2 , . . . , z p+3,2 , . . . , z p,3 , . . . , z p+3,3 , . . . , of the reproduced waveforms reproduced therefrom are averaged in the order of the sampling to be used as the data for the reproducing waveform. Here, the first suffix for z represents the order of the sampling, whereas the second suffix represents the number of iterated times. The use of the averaged data can remove the influence by the random noise on the reproduced waveform.

TECHNICAL FIELD

The present invention relates to a method for adjusting a recordingcondition to record and reproduce information by irradiating an opticalrecording medium with laser light, and to recording/reproducing methodand apparatus.

BACKGROUND TECHNOLOGY

Optical recording media include rewritable optical discs such as amagneto-optical disk and a phase-change optical disk. Typical recordingtechniques for recording the record data on such an optical recordingmedium include a mark position recording technique wherein the positionof the record mark has information, and a mark edge recording techniquewherein each of the front edge and rear edge of the record mark hasinformation.

The mark edge recording technique is suited to high recording density;however, the length of the record mark must be controlled with a higheraccuracy so as to allow the record data to be reproduced with a higherfidelity. The length of the record mark on the magneto-optical recordingdisk or the phase-change optical disk is determined by a temperaturerise of a recording film caused by irradiation with laser light. Thetemperature rise during the irradiation of the optical disk with thelaser light is changed depending on the structure and the linear speedof the disk.

During recording the record data on the optical recording disk, arecording technique, or so-called recording strategy technique, isgenerally used, wherein the waveform of the record data is divided intoa plurality of short pulses. For controlling the temperature rise tocontrol the mark length with a higher accuracy, the intensity and thewidth of each of the plurality of short pulses in the divided recordingpulse waveform (laser-modulated pulse waveform) must be optimizeddepending on the structure of the disk. “Shingaku Technical ReportMR93-55, CPM93-107, pp 13-18, 1993” describes an example of thetechniques for optimizing the recording strategy such as the pulse widthor pulse interval. In this technique, the lengths (time intervals)between the reference mark and the front and rear edges of the subjectmark to be measured are measured to determine the irradiation startingpoint and the pulse width of the recording pulse waveform.

However, as the record mark length recorded on the disk is reduced alongwith the development of the higher recording density, there sometimesoccurs a case where the signal amplitude of the reproduced waveform isreduced down to a level below the slice level of a slicer used formeasuring the record mark. This results in that the positions of thefront edge and rear edge of the subject mark cannot be measured with ahigher accuracy, and thus it is difficult to optimize the recordingstrategy by using the conventional technique such as described above.

As a technique for optimizing the recording strategy under the conditionof a high recording density, JP-A-2001-126260 describes a technique forderiving a pulse response from the reproduced waveform in the premisethat the recording/reproducing system is linear, to optimize therecording strategy. According to this conventional technique, h_(j)providing minimum values for ε′ are obtained as time-series data of thepulse response, the ε′ being expressed by the following formula (1):

$\begin{matrix}{{ɛ^{\prime} = {\sum\limits_{k}( {y_{l} - {\sum\limits_{j}{a_{l - j} \times h_{j}}}} )^{2}}},} & (1)\end{matrix}$

wherein a_(i) is a record data such as expressed by “1” or “0”, y_(i)are time-series data obtained by sampling the reproduced waveform basedon the clock frequency of the record data. The range for “j” isdetermined by the range where the time-series data h_(j) assume non-zerofinite values, and “k” is determined by the number of all thetime-series data of the reproduced waveform. Subsequently, h_(j) and theminimum values of ε′ in each recording pulse waveform are similarlyderived by changing the each recording pulse waveform, and the recordingpulse waveform providing the smallest value among the minimum values ofε′ is determined as the optimum recording pulse waveform.

In a linear recording/reproducing system, assuming that h_(j) is anoutput (generally referred to as “pulse response” or “impulse response”)of the recording/reproducing system during recording/reproducing a 1-bitdata, the reproduced waveform output at a specified time is expressed,if there is no noise, by the following formula (2):Σ(a_(i-j)×h_(j))   (2).The pulse response assumes different values for the recording densitiesand beam diameters or recording/reproducing conditions (such as tilt anddefocus). The above ε′ is the index for evaluating the nonlinearcomponents of the reproduced waveform, wherein a smaller value for ε′means a higher linearity of the reproduced waveform.

However, in the conventional technique as described above, if therecording density is extremely high to extensively reduce the signalamplitude of the reproduced waveform, the influence by noise cannot beneglected, and accordingly, the accuracy of the time-series data h_(j)of the pulse response and the minimum values of ε′ is degraded, wherebythere arise the problem that the optimization of the recording strategyis difficult.

In the conventional technique as described above, the clock frequency isextracted from the reproduced waveform, and the sampling of thereproduced waveform is performed using this clock frequency. Theextraction of the clock frequency from the reproduced waveform needs aPLL circuit, to thereby complicate the circuit structure. In addition,data having a data length of around 1000 bits, for example, is neededdepending on the circuit performance of the PLL, whereby there arisesthe problem that the signal processing takes a long time.

Although optimization of the recording pulse width is mainly describedin the conventional technique, the PLL circuit does not necessarilyoperate in order for adjusting the laser power if the laser power isinadequate, to raise the problem that the pulse response cannot bederived. Moreover, although the conventional technique uses only theabsolute value (the above ε′) of the deviation from the linearity, therearises a need for normalizing the deviation from the linearity in someformat, because the signal amplitude changes together with the change ofthe recording power in consideration of the adjustment of the recordingpower.

DISCLOSURE OF THE INVENTION

In view of the problems of the conventional technique, it is an objectof the present invention to provide a method for adjusting the recordingcondition by which the recording condition (recording strategy and laserpower) are optimized with accuracy and in a smaller time length even inthe case of a higher recording density, as well as recording/reproducingmethod and recording/reproducing apparatus for the optical information.

The present invention provides a method for adjusting a recordingcondition, including the steps of: irradiating an optical recordingmedium with laser light having a recording pulse waveform generatedbased on a recording signal, which is in synchrony with clock cycles, toform a record mark group on the optical recording medium; reading therecord mark group to obtain a reproduced waveform, and adjusting therecording condition by sampling the reproduced waveform at a periodshorter than a clock period to evaluate a linearity of the reproducedwaveform. In a preferred embodiment of the present invention, thetime-series data of the reproduced waveform for respective clock cyclesare obtained by interpolating the sampled values of the reproducedwaveform.

The present invention provides an adjusting condition for adjusting therecording condition by obtaining an index of the linearity by thefollowing formula (3):

$\begin{matrix}{ɛ = {\sum\limits_{l}( {y_{k} - {\sum\limits_{i}{a_{k - i} \times h_{i}}}} )^{2}}} & (3)\end{matrix}$(i being an integer satisfying 0≦i≦m), wherein [a₀, a₁, . . . , a_(k), .. . , a_(n−1), a_(n)] represent the time series data for the respectiveclock cycles of the clock for recording the optical recording medium,[y₀, y₁, . . . , y_(k), . . . , y_(n−1), y_(n)] represent time-seriesdata of the reproducing waveform for the respective clock cycles (nbeing an integer not smaller than zero, and k being an integersatisfying 0≦k≦n), and [h₀, h₁, . . . , h_(m)] represent pulse responsesof a recording/reproducing system corresponding to a specificrecording/reproducing condition (m being an integer satisfying 0≦m≦n).

Here, h_(i) is a value changing depending on the recording pulsewaveform. Accordingly, the value for ε can be adjusted by adjusting thish_(i) (or adjusting the recording condition). It is to be noted that asuitable recording condition can be obtained by adjusting the above ε toa smaller value.

The present invention provides, in another embodiment, a method foradjusting a recording condition, the method including: irradiating anoptical recording medium with laser light having a recording pulsewaveform generated based on a recording signal, which is in synchronywith clock cycles, to form a record mark group on the optical recordingmedium; and reading the record mark group to obtain a reproducedwaveform, characterized by obtaining an index of the linearity by thefollowing formula (4):

$\begin{matrix}{{R1} = {( {n + 1} ) \times \frac{\sum\limits_{i}h_{i}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}}} & (4)\end{matrix}$(i being an integer satisfying 0≦i≦m), wherein [a₀, a₁, . . . , a_(k), .. . , a_(n−1), a_(n)] represent the times-series data for the respectiveclock cycles of the clock for recording the optical recording medium,[y₀, y₁, . . . , y_(k), . . . , y_(n−1), y_(n)] represent time-seriesdata of the reproducing waveform for the respective clock cycles (nbeing an integer not smaller than zero, and k being an integersatisfying 0≦k≦n), and [h₀, h₁, . . . , h_(m)] represent pulse responsesof a recording/reproducing system corresponding to a specificrecording/reproducing condition (m being an integer satisfying 0≦m≦n).

Here, h_(i) is a value changing depending on the recording pulsewaveform. Accordingly, the value for R1 can be adjusted by adjustingthis h_(i) (adjusting the recording condition). It is to be noted that asuitable recording condition can be obtained by adjusting the above R1to a larger value.

In case for employing the above configuration, by setting so as tosatisfy 10×log R1>20-20(l/w), wherein w represents the beam diameter ofthe laser beam used for recording/reproducing information and lrepresents the shortest mark length to be recorded on theoptical-information recording medium, the bit error rate (b.e.r) can besuppressed down to a specified value or below. More specifically, in thepresent invention, the bit error rate can be also adjusted by adjustingR1.

The present invention provides, in another embodiment, a method foradjusting a recording condition, the method including: irradiating anoptical recording medium with laser light having a recording pulsewaveform generated based on a recording signal, which is in synchronywith clock cycles, to form a record mark group on the optical recordingmedium; and reading the record mark group to obtain a reproducedwaveform, characterized by obtaining an index of the linearity by thefollowing formula (5)

$\begin{matrix}{{R2} = \frac{\sum\limits_{k}y_{k}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}} & (5)\end{matrix}$(i being an integer satisfying 0≦i≦m), wherein [a₀, a₁, . . . , a_(k), .. . , a_(n−1), a_(n)] represent the times-series data for the respectiveclock cycles of the clock for recording on the optical recording medium,[y₀, y₁, . . . , y_(k), . . . , y_(n−1), y_(n)] represent time-seriesdata of the reproducing waveform for the respective clock cycles (nbeing an integer not smaller than zero, and k being an integersatisfying 0≦k≦n), and [h₀, h₁, . . . , h_(m)] represent pulse responsesof a recording/reproducing system corresponding to a specificrecording/reproducing condition (m being an integer satisfying 0≦m≦n).

Here, h_(i) is a value changing depending on the recording pulsewaveform. Accordingly, the value for R2 can be adjusted by adjustingthis h_(i) (adjusting the recording condition). It is to be noted that asuitable recording condition can be obtained by adjusting the value forR2 to a larger value. In addition, the bit error rate can be suppresseddown to the specified value or below by adjusting R2 so as to satisfy10×log R2>21−20(l/w), wherein w represents the beam diameter of thelaser beam used for recording/reproducing information and l representsthe shortest mark length to be recorded on the optical-informationrecording medium, the bit error rate (b.e.r) can be suppressed down to aspecified value or below. More specifically, in the present invention,the bit error rate can be also adjusted by adjusting R2.

In addition, the present invention may include, in the recordingcondition adjusting step, either the steps of recording a plurality ofrecord mark groups on the optical recording medium by using a singlerecording pulse waveform, reproducing the same to sample a plurality ofreproduced waveforms, and averaging the sampled values, or the steps ofrecording a record mark group by using a recording pulse waveform on theoptical recording medium, reproducing the same for a plurality of timesto sample a plurality of reproduced waveforms, and averaging the sampledvalues. In this case, a more accurate adjustment can be obtained.

Further, in the recording condition adjusting method according to thepresent invention, especially in the case of the medium being aphase-change optical recording medium, an overwrite operation may beconducted twice or more before the reproducing, upon obtaining thereproduced waveform. In this case, the recording condition can beadjusted more accurately.

A recording/reproducing apparatus according to the present inventionemploys the recording condition adjusting method(s) as described above.

More specifically, the present invention provides an apparatus forrecording/reproducing optical information, including an optical headirradiating an optical recording medium with laser light to receivereflected light therefrom, a laser drive for changing an opticalintensity of a laser output thereof, and a control section having thefunctions of: converting a recording signal into a recording pulsewaveform to transmit the same to the laser drive; sampling a reproducedwaveform, reproduced from record marks on the optical recording medium,at a period shorter than a clock period; interpolating the sampledvalues; evaluating a difference between a waveform obtained byconvolution of pulse responses determined from the reproduced waveformand the recording signal and a waveform obtained, by sampling thereproduced waveform and interpolating sampled values thereof, to adjusta width or power of the recording pulse waveform. In therecording/reproducing apparatus according to the present invention, theabove ε or the above R1 or R2 may be evaluated to adjust the recordingpulse waveform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an optical-information recording apparatusaccording to an embodiment of the present invention.

FIG. 2 is a timing chart showing the waveforms of the record data andrecording pulses used for recording in the optical-information recordingapparatus of FIG. 1.

FIG. 3 is a timing chart showing the iteratively reproduced waveformsreceived in the CPU of the optical-information recording apparatus ofFIG. 1.

FIG. 4 is a timing chart of the waveform obtained by averaging theiteratively reproduced waveforms shown in FIG. 3.

FIG. 5 is a sectional view of an example of the optical disk used forrecording in the optical-information recording apparatus of FIG. 1.

FIG. 6 is a timing chart showing the waveforms of the record data andrecording pulse, explaining optimization of the recording strategy in afirst example of the present invention.

FIG. 7 is a graph showing the relationship between the top pulse widthof the recording pulse waveform shown in FIG. 6 and an index I (I2).

FIG. 8 is a graph showing the relationship between the number ofiteration times of the recording pulse waveform shown in FIG. 6 and theindex I (I2).

FIG. 9 is a graph showing the relationship between the top pulse widthof the recording pulse waveform shown in FIG. 6 and the index I (I2) andbetween the pulse width and ε.

FIG. 10 is a graph showing the relationship between the top pulse widthof the recording pulse waveform shown in FIG. 6 and the bit error rate.

FIG. 11 is a graph showing the relationship between the cooling pulsewidth of the recording pulse and the index I (I2), and the relationshipbetween the pulse width and the bit error rate in a second example.

FIG. 12 is a graph showing the relationship between the laser power andthe index I (I1, I2, I3) and the relationship between the laser powerand the bit error rate.

FIG. 13 is a graph showing the relationship between the laser power andthe index I1 upon changing the number of overwrite times.

FIG. 14 is a graph showing the relationship between the laser power andindexes I (I1, I2, I3) and the relationship between the laser power andthe bit error rate.

FIG. 15 is a graph showing the relationship between the length of thepulse response and the indexes (I1, I2 and I3).

FIG. 16 is a graph showing the relationship between the index I1 forachieving the specified bit error rate and the shortest mark recorded onthe disk.

FIG. 17 is a graph showing the relationship between the index I2 forachieving the specified bit error rate and the shortest mark recorded onthe disk.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detailbased on the embodiment of the present invention with reference toaccompanying drawings.

FIG. 1 shows an optical-information recording apparatus according to anembodiment of the present invention. The optical-information recordingapparatus of the present embodiment employs a process of deriving pulseresponse from a reproduced waveform and adjusting therecording/reproducing condition based on the information obtained fromthe pulse response. For deriving the pulse response, time-series data ofthe reproduced waveform for clock cycles is needed. The clock cycles areextracted from the reproduced waveform, in general, by using a PLL(phase-locked loop). In this procedure, data having a specified lengthand a time length for the circuit processing are needed, as well as thePLL circuit. In the present embodiment, the extraction of the clockcycles by using a PLL circuit is not conducted, and sampling of thereproduced waveform is conducted at a period less than the clock period(period shorter than the clock period). The time-series data of thereproduced waveform obtained by this sampling are fetched in the CPU,wherein time-series data of the reproduced waveform for the clock cyclesare calculated by an interpolation technique from the input time-seriesdata. The pulse response is derived from the time-series data of thereproduced waveform for the clock cycles thus obtained. Thereby, the PLLcircuit is not needed to simplify the circuit configuration, and thetime length for derivation of the pulse response can be reduced. Inaddition, even if the laser power is deviated from an optimum laserpower to cause a malfunction of the PLL circuit, the data of thereproduced waveform for the clock cycles can be obtained. Thus, thelinearity of the reproduced waveform can be evaluated.

It is to be noted that the rotational speed of the optical disk may befluctuated by some external disturbance, to thereby cause a situationwhere the rotational speed differs between at the time of recording andat the time of reproducing. In such a case, due to the difference in thereference clock time between at the recording and at the reproducing,correct data cannot be obtained by the linear interpolation of thewaveform data at the reproducing based on the clock time at therecording. However, even in this case, after assuming a plurality ofclock times, the above “ε”, R1 and R2 are obtained by interpolating thewaveform data for respective clock times thus assumed and then theminimum value for “ε” or the maximum values for R1 and R2 are examined,whereby the linearity of the waveform can be evaluated together withcalculating the correct clock time at the reproducing.

On the other hand, as the record mark length recorded on the disk isreduced along with development of a higher recording density, the signalamplitude of the reproduced waveform is reduced to cause a largerinfluence thereon by noise. This noise acts to provide a pulse responsedifferent from the inherent pulse response that therecording/reproducing system has, or provide an uncertainty tocalculation of the pulse response. Therefore, the difference between thecalculated result obtained by convolution processing of the pulseresponse and the record data and the reproduced waveform is eitherdifferent from that in the case of the absence of noise, or uncertain,whereby the recording pule waveform selected is different from thewaveform having the optimum recording strategy. The present inventor hasfound that, by iteratively recording a single recording pulse waveformfor a plurality of times on the optical recording medium to form therecord marks thereon and averaging a plurality of reproduced waveformsreproduced from these record marks, the influence by the random noisecan be reduced to allow deriving of the recording pulse waveform havingthe optimum recording strategy, as will be detailed hereinafter.

As shown in FIG. 1, the recording/reproducing apparatus 1 according tothe present embodiment includes an optical head 3 for irradiating anoptical disk 2 with laser light, an LD driver 4 provided as a driver forchanging the intensity of the laser light, and a CPU 5 provided as acontrol section. The CPU 5 has functions of allowing the LD driver 4 andthe optical head 3 to convert the record data into a variety ofrecording pulse waveforms to form record marks on the optical disk,allowing the optical head to reproduce the record mark information onthe optical disk to obtain reproduced waveforms, deriving pulseresponses from the reproduced waveforms reproduced from the recordingpulse waveforms, adjusting the recording pulse waveform so as tominimize the difference between the waveform obtained by convolution ofthe pulse responses and the record data and the reproduced waveform, tothereby obtain an optimum recording waveform, and averaging reproducedwaveforms. These functions are implemented by software stored in the CPU5.

The record data used for determining the recording strategy may beobtained by suitably modulating the typical random data such asM-sequential data, for example. It is sufficient that the record datahave a length of around 200 bits in order to accurately derive the pulseresponse.

The averaging processing of the reproduced waveforms may be such thatrecord marks recorded on a single track are reproduced for a pluralityof times and the resultant reproduced waveforms are averaged. However,for reducing the time length for the data acquisition, it is morepreferable that a plurality of iterated patterns having the samerecording pulse waveform be recorded on a single track, and bereproduced therefrom and subjected to an averaging processing. If therecording area is too long, the signal amplitude may be fluctuated evenin the circumference of the single track, to thereby cause a difficultyin an accurate averaging processing. To the contrary, since the recorddata used in the present embodiment has a data length of around 200 bitsat most, the occupied area thereof is only a small part of thecircumference of the single track, not to cause a fluctuation of thesignal amplitude, assuming that a single bit length is 0.5 μm and, forexample, and 10-time iterated patterns are used therein.

FIG. 2 shows part of the record data and the recording pulse waveformtogether with the clock signal. T is the clock period. The recordingpulse waveform having an optimum recording strategy is derived in theprocess as described hereinafter. First, a recording pulse waveform isrecorded on the optical disk by using laser light from the optical headto form record marks, the information of which is read out to generatethe reproduced waveform. The reproduced waveform thus reproduced issampled at a period not longer than the clock period, and received inthe CPU.

FIG. 3 shows parts of the reproduced waveforms reproduced after therecording pulse waveform of FIG. 2 is iteratively recorded on a singletrack for three times. In FIG. 3, for a simplification purpose of thedrawing, only a pulse of the reproduced waveform corresponding to therecord data portion of first 5T length of the record data of FIG. 2 isshown for each of the iterations. The z_(p,1), . . . , z_(p+3,1),z_(p,2), . . . , z_(p+3,2), and z_(p,3), . . . , z_(p+3,3) aretime-series data of the reproduced waveform for each of the iterations.Here, the first suffix of z represents the order of sampling for each ofthe iterations, whereas the second suffix of z represents the number ofiterated times. Subsequently, the three data, z_(p,1), . . . ,z_(p+3,1), z_(p,2), . . . , z_(p+3,2), and z_(p,3), . . . , z_(p+3,3),of the reproduced waveforms for the same value of p are averaged toobtain time series data, . . . , z_(p), . . . , z_(p+3), . . . , of theaveraged reproduced waveform.

FIG. 4 shows the time-series data . . . z_(p) . . . of the averagedreproduced waveform as obtained above by plotting the same with dots.Subsequently, time-series data y_(k) at the transition between “0” and“1” of the clock signal are obtained by interpolating the preceding andsucceeding time-series data z_(p). The points indicated by the downwardarrows in FIG. 4 mean the points of the interpolation for providing they_(k). For performing the interpolation with ease, for example, areference pulse should be added to the top of the record data, forexample, and it is sufficient that, upon the reproducing, thetime-series data be extracted by using the reproduced signal from thereference mark recorded by the reference pulse, as the start point. Thek is an integer satisfying 0≦k≦n, wherein n is an integer not smallerthan zero. The number of all the time-series data y_(k) is (n+1). Here,it is assumed that ε is defined by the formula (3) described above.

$\begin{matrix}{ɛ = {\sum\limits_{l}( {y_{k} - {\sum\limits_{i}{a_{k - i} \times h_{i}}}} )^{2}}} & (3)\end{matrix}$wherein “i” is an integer satisfying 0≦i≦k.

Here, a_(k-i) is record data. If the time-series data h_(i) providing aminimum for ε is obtained by, for example, using a least-squares methodor solving the partial differential equation ∂ε/∂h_(i)=0, the resultanttime-series data h_(i) provide time-series data of the pulse response“h” of the recording/reproducing system with a higher-accuracy,depending on the maximum of k, i.e., number of the time-series datay_(k). The range within which the time-series data h_(i) of the pulseresponse “h” assumes a non-zero finite value is generally around i=2 to20, depending on the circuit characteristic, optical headcharacteristic, recording density etc. of the recording/reproducingsystem, and for “i” above such a range, h_(i) may be practically assumedas zero. Therefore, it is sufficient that the number of summation forthe “i” be about twenty at most.

Subsequently, by performing the above steps while changing the recordingstrategy, the time-series data of the pulse response and the minimum ofε for that case are obtained. The recording strategy providing the leastvalue among the minimums of ε, which are obtained by consecutivelychanging the recording strategy similarly, is the optimum recordingstrategy. The fact that ε is small means that the linearity between therecord data and the reproduced waveform data is high, and thus meansthat a reproduced waveform near the reproduced waveform expected by themark edge recording scheme can be obtained. Although it is desired thatthe value of ε be zero in an ideal case, the perfect zero for the εvalue is difficult to achieve due to the influence by noise, such asdisk noise, laser noise, circuit noise etc., on the reproduced waveform.Thus, the recording strategy providing the least value for ε among thestrategies thus changed may be called the optimum recording strategy.

As an index of the optimization of the recording strategy, each of R1and R2 defined by the formulas (4) and (5):

$\begin{matrix}{{{R1} = {( {n + 1} ) \times \frac{\sum\limits_{i}h_{i}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}}};\mspace{14mu}{and}} & (4) \\{{{R2} = \frac{\sum\limits_{k}y_{k}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}},} & (5)\end{matrix}$as well as each of I1 and I2 defined by the following formulas (6) and(7):I 1=10×log R 1   (6) andI 2=10×log R 2   (7)may be used instead of ε.

As apparent from the formulas (4) and (5), the index R (R1 or R2) is thereciprocal of the normalized index ε normalized using the informationobtained from the reproduced waveform. The index I (I1, I2) is thelogarithmic expression of the index R (R1, R2). Although theoptimization of the recording strategy is performed by adjusting thepulse width or pulse interval of the recording pulse waveform, the totalsum of the squares of the time-series data y_(k) of the reproducedwaveform is not significantly changed by changing these pulse width andpulse interval to some extent. More specifically, the absolute value ofy_(k) assumes a larger value only for the case of a long mark or a longspace, and the adjustment of the recording strategy is needed mainly forthe case of a short mark or a short space. Thus, the maximum of R or I,if used instead of the minimum of ε, scarcely affects the results. Thisprovides an advantage that R and I are dimensionless amounts independentof the gain, reproducing power etc. of the reproducing circuit,differently from the ε having a unit corresponding to the square of thesignal amplitude to change its amount depending on the gain, reproducingpower etc. of the reproducing circuit.

On the other hand, in consideration of the adjustment of the laser powerused for recording information, since the signal amplitude changes withthe change of the recording power, the deviation from the linearityshould be normalized in some way. More specifically, since it isconsidered that a smaller recording power may involve the case whereinthe absolute vale of ε is smaller and the signal amplitude itself isextremely small, there is a possibility that the laser power providingthe minimum value for ε does not necessarily coincide with the optimumlaser power. The present inventor found that the above R1 or R2 (or, I1or I2) may be used as the index of normalizing ε for adjusting the laserpower. R1 uses the energy of the pulse response multiplied by the bitnumber evaluated therefor as the normalized signal amplitude, whereas R2uses the total sum of the energy of the reproduced waveform as thenormalized signal amplitude.

Any of the indexes R1 and R2 may be used for adjusting the laser power.Since the energy of the reproduced waveform used in R2 includes noisecomponent or nonlinear component as it is, adjustment of the laser powermay be considered difficult to achieve in the case where chromatic noiseis extremely high or the reproduced waveform has a considerablenon-linearity. For this reason, R1 using only a linear component as thesignal energy is more preferable. In stead of R1, R3 defined by thefollowing formula (8):

$\begin{matrix}{{R3} = {( {n + 1} ) \times \frac{h_{i\_ max}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}}} & (8)\end{matrix}$may be used. The R3 represents the energy of the pulse response by thesquare of the amplitude. In the formula (8), h_(i) _(—) _(max)represents the amplitude of the pulse response. As the index ofadjusting the recording condition, R3 may be used as it is, or in theform of I3, which is the logarithm of R3, similarly to I1 and I2.

Upon adjusting the laser power, the iterative recording of the samerecord data need not be necessarily performed for an average processing.This is because, if the laser power deviates from the optimum laserpower in the case of adjusting the laser power for the overwriteoperation on the phase-change optical disk, for example, then theun-erased component of the preceding data existing before the overwriteoperation is dominant over the noise, which fact enables a linearevaluation of the waveform without the need for suppressing the noisecomponent.

EXAMPLE 1

FIG. 5 is a sectional view of an optical disk used in Example 1according to the embodiment of the present invention. As depicted inFIG. 5, the optical disk used in this example includes reflector film11, protective film 12, recording film 13, protective film 14 andoptical transmission film 15, which are layered in this order on aplastic substrate 10. The recording film 13 is formed as a phase-changerecording medium. The plastic substrate 10 is made of polycarbonate, andthe pitch of the guide grooves thereof is 0.32 μm. The optical head ofthe present example has a laser wavelength of 400 nm and a NA (numericalaperture) value of 0.85.

FIG. 6 shows parts of the recording signal and recording pulsewaveforms, explaining optimization of the recording strategy inExample 1. FIG. 7 is a characteristic chart showing the relationshipbetween the top pulse width of the recording pulse waveform of FIG. 6and the index I2. FIG. 8 is a characteristic chart showing therelationship between the number of iteration times (number of averagetimes) of the recording pulse waveform of FIG. 6 and the index I2. FIG.9 is a characteristic chart showing the relationship between the toppulse width of the recording pulse waveform of FIG. 6 and the index I2as well as the relationship between the top pulse width and ε. FIG. 10is a characteristic chart showing the relationship between the top pulsewidth of the recording pulse waveform of FIG. 6 and the bit error rate.

Recording was performed on the optical disk at a clock frequency of 90MHz while rotating the disk at a linear speed of 5.5 m/s. The laserlight from the optical head was incident from the optical transmissionfilm side of the optical disk, whereby record marks were formed on aland portion between guide grooves. The recording power and erasingpower were 4 mW and 1.5 mW, respectively. The diameter of the opticalbeam on the optical disk was 0.4 μm. In addition, for adapting to themark edge recording scheme, M-series pseudorandom data having a lengthof 200 bits as described above were converted to 1-7 RLL (run lengthlimited), followed by NRZI (NonReturn-to-Zero-Inverted)modulation-encoding to generate record data. In this case, seven kindsof record marks (hereinafter referred to as “2T record mark” to “8Trecord mark”) having lengths of 2T to 8T in terms of reproduced timelength were formed on the disk, wherein the shortest record mark had alength of 0.12 μm. T is the clock period, wherein T=11.11 ns in thisexample. The extraction of the reproduced waveform was conducted every10 ns.

The measurement of the b.e.r. was performed by recording and reproducingM-series pseudo-random data having a length of 10⁶ bits for eachstrategy.

FIG. 6 shows the record data having a pulse width of 3T and therecording pulse waveform corresponding thereto, for explaining therecording strategy. Hereinafter, the recording pulse waveformcorresponding to the record data having a pulse width of 3T is referredto as a 3T signal. The recording pulse waveform corresponding to therecord data having another length is similarly referred to. As shown inFIG. 6, the recording pulse waveform is a pulse signal including,succeeding to the zone Tst of an erasing power level: a top pulse havinga recording power level and a pulse width of Ttop; a multi-pulse sectionincluding a low-level pulse having a pulse width of Tsmp and a biaspower level, and a high-level pulse having a pulse width of Tmp and arecording power level; and a cooling section having a pulse width ofTcl. Although a laser power of around 0.1 to 0.5 mW generally exists inthe cooling pulse, even a complete zero laser power scarcely affects theresults to be obtained. The zone Tst and the pulse widths Ttop, Tsmp,Tmp, Tcl may be used as recording compensation parameters for optimizingthe recording strategy.

Among the adjustments of those recording compensating parameters,adjustments of the recording compensating parameters of 2T signal and 3Tsignal are especially needed in the high-density recording condition.The recording compensating parameters of 4T signal to 8T signal are notnecessarily adjusted for each of these signals: for example, if the 4Tsignal is optimized, other signals can be optimized by increasing orreducing the number of pulses in the multi-pulse section.

Hereinafter, by exemplifying the 3T signal, the step of optimizing therecording strategy by changing the pulse width Ttop of the top pulsethereof will be described. Table 1 shows each parameter used in thepresent example. In the present example, only the preceding duration Tstbefore starting the top pulse of the 3T signal and the pulse width Ttopof the top pulse are changed, with the recording compensation parametersof the 2T signal and 4T to 8T signals being fixed. In Table 1, thenumber of pairs each including the low-level pulse having a pulse widthof Tsmp and the high-level pulse having a pulse width of Tmp in themulti-pulse section is increased one by one from the 3T signal towardthe 8T signal, such as two pairs in the 4T signal, three pairs in the 5Tsignal, . . . .

TABLE 1 Tst Ttop Tsmp Tmp Tcl 2T 1.65T 0.35T 0.3T 3T 2T–Ttop 0.3T–0.5T0.5T 0.5T 0.4T 4T–8T  0.5T  0.5T 0.5T 0.5T 0.4T

First, the record data generated as above are converted into therecording pulse waveform having a configuration such as shown in FIG. 2,followed by recording 8-time-iterated patterns of the recording pulsewaveform on the optical disk and then examining the number of averagingprocessings needed for optimizing the recording strategy. During thisprocedure, a 10T reference mark was recorded at the top of eachrecording pulse waveform for each of iterations of the recording pulsewaveform, and time series data of the reproduced waveform were fetchedusing the reproduced waveform from the 10T reference mark as thestarting point. This procedure was employed for improving thepositioning accuracy for the data extraction. It is to be noted that thelength of the reference mark or space used for the starting point is notlimited to a length of 10T, and it is sufficient that the length bestably detectable (preferably longer than the diameter of the opticalbeam) and it have a pattern not used for the record data.

FIG. 7 shows the index I2 plotted while changing the pulse width Ttop ofthe top pulse of the 3T signal from 0.3T to 0.5T. In FIG. 7, the fourcurves are obtained by averaging one, two, three and eight among theeight iteratively recorded pulse waveforms. As shown in FIG. 7, for thecase of averaging processing wherein the number of the averaged is one(no averaging processing) or two, the value for the index I2 is smalldue to the influence by noise, and also the change of the index I2 alongwith the change of the pulse width Ttop of the top pulse constitutingthe recording compensation parameter for the optimization of therecording strategy is not clear. Therefore, it is difficult to determinethe optimum recording strategy by using the averaging processing whereinthe number of the averaged is two or less. For the averaging processingwherein the number of the averaged is three or more, the index I2 has alarger value, and the change of the index I2 along with the change ofthe pulse width Ttop of the top pulse is clear.

In addition, in the averaging processing wherein the number of theaveraged is three or more, the value of the index I2 scarcely depends onthe number of the averaged. FIG. 8 shows the index I2 plotted againstthe number of the averaged in the 3T signal wherein the pulse width Ttopof the top pulse is 0.4T. As shown in FIG. 8, the index I2 changes inthe averaging processing wherein the number of the averaged is two orless, whereas the index I2 is substantially fixed in the averagingprocessing wherein the number of averaged is three or more. Accordingly,the influence by noise is substantially completely removed by theaveraging processing wherein the number of the averaged is three ormore.

FIG. 9 shows the indexes I2 and ε plotted while changing the pulse widthTtop of the top pulse of the 3T signal from 0.3T to 0.5T. The values forthe indexes I2 and ε were obtained by averaging the 3-time-iteratedpatterns of the recording pulse waveform. As shown in FIG. 9, when thepulse widths Ttop of the top pulses are all 0.4T, the index I2 assumes amaximum and the index ε assumes a minimum. This means the index I2 canbe properly used instead of the index ε.

FIG. 10 shows the bit error rate b.e.r. plotted while changing the pulsewidth Ttop of the top pulse of the 3T signal from 0.3T to 0.5T. Thevalue for the bit error rate were obtained by averaging 3-times-iteratedpatterns of the recording pulse waveform. As shown in FIG. 10, the biterror rate assumes a minimum when the pulse width Ttop of the top pulseis 0.4T. This pulse width 0.4T of the top pulse is equal to the pulsewidth 0.4T of the top pulse at which the index I2 of FIG. 7 assumes amaximum.

EXAMPLE 2

FIG. 11 is a characteristic chart showing the relationship between thepulse width of the cooling section of the recording pulse waveform andthe index I2 as well as the relationship between the pulse width and thebit error rate, explaining optimization of the recording strategy inExample 2 of the present invention.

Recording was performed on the optical disk at a clock frequency of 70MHz while rotating the disk at a linear speed of 5.5 m/s. The recordingpower and erasing power were 4 mW and 1.5 mW, respectively. The diameterof the optical beam on the optical disk was 0.4 μm. The record data usedfor adjusting the strategy and measuring the b.e.r. were similar tothose used in Example 1 except that the clock frequency was changed. Inthis case, 2T to 8T record marks were formed on the disk, similarly toExample 1, with the shortest record mark being 0.16 μm long. The clockperiod T was T=14.29 ns. The sampling of the reproduced waveform wasconducted every 10 ns.

In the present example, the pulse width Tcl of the cooling section inthe 2T signal was selected as the recording compensation parameter to beadjusted. Table 2 shows each parameter used in the present example. Inthe present example, only the pulse width Tcl in the 2T signal waschanged from 0.2T to 0.4T, with the recording compensation parameters inthe 3T to 8T signals being fixed. In Table 2, the number of pulse pairsin the multi-pulse section is one in the 3T signal, and the number ofpairs is increased one by one from the 3T signal to the 8T signal.

TABLE 1 Tst Ttop Tsmp Tmp Tcl 2T 1.65T 0.35T 0.2T–0.4T 3T  1.6T  0.4T0.5T 0.5T 0.4T 4T–8T  1.5T  0.5T 0.5T 0.5T 0.4T

The number of iteration times of the recording pulse waveform was three,and the index I2 and bit error rate b.e.r. were calculated from theaveraged values of the 3-time-iterated patterns. FIG. 11 shows the indexI2 and bit error rate thus obtained, which are plotted against the pulsewidth Tcl of the cooling section in the 2T signal. As shown in FIG. 11,0.3T is optimum as the pulse width Tcl of the cooling section in the 2Tsignal.

Although the data for I2 is described herein as the representative of alinear and normalized index in the Example 1 and Example 2, I1 or I3also has the strategy dependence similarly to I2, and it was confirmedthat optimization of the strategy was possible using I1 or I3.

EXAMPLE 3

A phase-change optical disk, wherein protective film, recording film,protective film and reflector film were consecutively layered on a0.6-mm-thick plastic substrate and a ultraviolet-ray-cured resin layerwas formed on the reflector film, was used to investigate therelationship between the laser power and I1, I2 and I3. The recordingfilm was made of a phase-change recording medium. Polycarbonate was usedas the plastic substrate, wherein the pitch of guide grooves was 0.42μm. In addition, the laser wavelength of the optical head was 405 nm,and the NA value thereof was 0.65.

Recording was performed on the optical disk at a clock frequency of 60MHz while rotating the disk at a linear speed of 5.2 m/s. The recordingwas performed while changing the laser power, with the ratio of therecording power to the erasing power being at 2.4. The diameter of theoptical beam on the optical disk was 0.52 μm. As for the record data,the data used for adjusting the laser power were random data having alength of 200 bits similarly to Example 1, whereas the record data usedfor measuring the b.e.r. was record data having a length of 10⁶similarly to Example 1, wherein only the clock frequency was changed. Inthis procedure, 2T to 8T record marks were formed similarly to Example1, although the shortest record mark had a length of 0.17 μm. The clockperiod T was T=16.66 ns. The reproduced waveform was fetched at every 15ns.

The procedure of overwriting by each of the laser powers for ten timeswere conducted at the each of the laser powers, thereby obtaining theb.e.r., R1, R2 and R3 for the each condition. FIG. 12 shows the resultsthereof. In the present example, the averaging processing was notconducted. In the present example, the averaging processing scarcelyimproved the values for R1, R2 and R3. This was considered due to thefact that the linearity of the waveform was not white noise, and theremaining un-erased component of the preceding data existing before theoverwrite operation dominated the linearity of the waveform.

The laser power shown in FIG. 12 is normalized, wherein the laser powercorresponding to “1” means a recording power of 6 mW and an erasingpower of 2.5 mW. Similarly, the laser power corresponding to “1.2” meansa recording power of 7.2 mW and an erasing power of 3 mW. It isunderstood from FIG. 12 that the laser power providing a best value forthe b.e.r. and the laser power providing maximum values for R1, R2 andR3 coincide with each other and thus the laser power can be effectivelyadjusted by examining the values for R1, R2 and R3 (logarithms I1, I2and I3 of the respective values thereof are shown in FIG. 12) whilechanging the laser power.

In addition, measurements were conducted using the above phase-changeoptical disk while changing the number of overwrite times for the eachof the laser powers, thereby examining the relationship between thelaser power and R1, R2 and R3 in the case of changing the number ofoverwrite times. FIG. 13 shows the results for I1 (R1) as the typicalexample. Again, in this measurement, the averaging processing was notconducted.

As understood from FIG. 13, the maximum value for I1 (R1) is difficultto find by one overwrite time (the first recording), and thus it isdifficult to optimize the laser power. This is considered due to thefact that the first recording is not affected by the preceding recorddata at all, which inherently exists in the overwrite operation. Morespecifically, if the erasing laser power is inadequate, the remainingun-erased component of the preceding record data generally appears asthe distorted component of the signal and thus the linearity of thewaveform largely changes, whereas the remaining un-erased component ofthe preceding data does not exist in the first recording. Although thedrawing does not specifically show, similar results were obtained as toR2 and R3. Therefore, for optimizing the laser power for thephase-change optical disk by examining the values for R1, R2 and R3, atleast two overwrite times are necessary.

EXAMPLE 4

A phase-change optical disk, wherein protective film, recording film,protective film and reflector film were consecutively layered on a0.6-mm-thick plastic substrate and a ultraviolet-ray-cured resin layerwas formed on the reflector film, was used to investigate therelationship between the laser power and I1, I2 and I3. The recordingfilm was as thick as 30 nm thick, and the reflector film was as thin as10 nm thick, to obtain a disk configuration wherein the heat dissipationcapability was low and the edge shift (nonlinear component) was largeduring the recording. Polycarbonate was used as the plastic substrate,wherein the pitch of guide grooves was 0.42 μm. In addition, the laserwavelength of the optical head was 405 nm, and the NA value thereof was0.65.

Recording was performed on the optical disk at a clock frequency of 60MHz while rotating the disk at a linear speed of 5.2 m/s. The recordingwas performed while changing the laser power, with the ratio of therecording power to the erasing power being at 2.4. The diameter of theoptical beam on the optical disk was 0.52 μm. As for the record data,the record data were similar to those in Example 3, and only the clockfrequency was changed. In this procedure, 2T to 8T marks were formed,although the shortest record mark had a length of 0.17 μm. The clockperiod T was T=16.66 ns. The reproduced waveform was fetched at every 15ns.

The procedure of overwriting by each of the laser powers for ten timeswas conducted at the each of the laser powers, thereby obtaining theb.e.r., R1, R2 and R3 for the each condition. FIG. 15 shows the resultsthereof. In the present example, the averaging processing was notconducted.

As understood from FIG. 14, although the laser power providing maximumvalues for R2 and R3 and the laser power providing a minimum value forthe b.e.r. coincide with each other, as for R1, the laser powerproviding maximum value for R1 and the laser power providing a minimumvalue for the b.e.r. do not coincide with each other. This is considereddue to the fact that although the edge shift is larger when the laserpower is higher, the index of the linearity as to R1 is normalized bythe signal component including the edge shift. Thus, for optimizing thelaser power, it is more preferable to use R2 or R3.

EXAMPLE 5

The length of the pulse response to the reproduced waveform obtained inExample 3 was changed from 5T to 20T (T: channel clock) to obtain thevalues for I1, I2 and I3, thereby examining the relationship between thelength of the pulse response and I1, I2 and I3. FIG. 15 shows theresults thereof. It is to be noted that the data shown in FIG. 15 wereobtained for the reproduced waveform data obtained for the laser power 1in Example 3. As understood from FIG. 15, the case where I1, I2 and I3assume approximately saturated values arises when the pulse response hasa length of 15T or more, and if the length is smaller, the valueslargely vary so that the linearity cannot be evaluated with accuracy.

EXAMPLE 6

The data recorded in Example 3 were reproduced at a linear speed of 5.3m/s, and data for I1, I2 and I3 were calculated while changing the clockperiod for the interpolation. Since the recording was performed at alinear speed of 5.2 m/s under the condition of clock period at 16.66 ns,as described in connection with Example 3, the reproduction at a linearspeed of 5.3 m/s corresponds to an accurate clock period of 16.35 ns.After I1, I2 and I3 were calculated while changing the clock period forthe interpolation of the reproduced waveform from 15 ns to 18 ns with astep of 0.05 ns, it was confirmed that I1, I2 and I3 assumed maximumvalues in the case where the clock period was assumed 16.35 ns.Accordingly, even if some external disturbance causes a fluctuation ofthe rotational speed of the optical disk to vary the rotational speedbetween the time of recording and the time of the reproducing, a correctclock period for the reproducing can be calculated along with theevaluation of the linearity of the waveform by assuming a plurality ofclock periods and interpolating the waveform data in the assumed clockperiods.

EXAMPLE 7

FIGS. 16 and 17 show the characteristic charts between the shortest bitlength and the index I1 and the shortest bit length and the index I2,respectively, which were obtained by optimizing the recording strategyin Example 2 of the present invention.

The phase-change optical disk used in Example 1 was rotated at a linearspeed of 5.5 m/s while changing the clock frequency by using opticalheads having a wavelength of 405 nm and having NA=0.8 and NA=0.75, tothereby conduct recording while changing the shortest record mark lengthrecorded on the optical disk, whereby the relationship between the laserpower and the b.e.r. was examined. Similarly, the phase-change opticaldisk used in Example 3 was rotated at a linear speed of 5.5 m/s whilechanging the clock frequency by using optical heads having a wavelengthof 405 nm and having NA=0.65 and NA=0.6, to thereby conduct recordingwhile changing the shortest record mark length recorded on the opticaldisk, whereby the relationship between the laser power and the b.e.r.was examined. The beam diameter was 0.6, 0.52, 0.46, and 0.4 mm in thecases of NA=0.6, 0.65, 0.75 and 0.85, respectively.

Upon changing the laser power, the ratio of the recording power to theerasing power was fixed, and the overwrite operation was conducted for10 times for each of the laser powers during the change of the laserpower, before I1, I2 and the b.e.r. were measured. As for the recorddata, data having a length of 200 bits was used, similarly to Example 1,to measure I1 and I2, and data having a length of 10⁶ bits similarly toExample 1 was used to measure the b.e.r. The shortest mark length waschanged by changing the clock frequency.

In FIGS. 16 and 17, the indexes I1 and I2 providing a bit error rate of1×10⁻⁴ are plotted for each shortest record mark length L. The reasonfor employing a bit error rate of 1×10⁻⁴ as a reference is that themaximum of the bit error rate within which the error correction ispossible (the system operates without a malfunction) by using an errorcorrection such as a reed solomon is generally 1×10⁻⁴. The index I (I1,I2) is approximately on a straight line, and the area of the sheet abovethe straight line, a boundary, corresponds to the area of the index Iwhich provides a bit error rate of 1×10⁻⁴ or less. More specifically, ifthe condition where I1≧20−aL and I2≧21−aL is satisfied, then the biterror rate is not higher than 1×10⁻⁴. It is also understood that thevalue for “a” becomes smaller as the beam diameter becomes larger. Thus,the relationship between the value for “a” and the beam diameter wasexamined, to reveal that “a” was in inverse proportion to the beamdiameter, and that the straight lines in FIGS. 16 and 17 wereapproximated by I1=20−20(L/w) and I2=21−20(L/w), respectively. That is,if the condition where I1=20−20(L/w) and I2=21−20(L/w) are satisfied,the bit error rate will be not higher than 1×10⁻⁴. Thus, adjustment ofthe laser power so as to satisfy this condition provides a bit errorrate of not more than 1×10⁻⁴.

In the recording process and the recording apparatus for the opticalinformation, according to the present embodiment as described above, therecording condition is optimized by determining the pulse response so asto minimize the difference between the reproduced waveform obtained byrecording and reproducing the recording pulse signal obtained byrecording strategy processing of the record data and the waveformobtained by convolution processing of the record data and the pulseresponse. Upon the optimization, since the recording condition isoptimized by sampling the reproduced waveform at a period shorter thanthe clock period, the recording strategy is optimized within a shortperiod of time without using a complicated circuit configuration.

In addition, since the clock period is not extracted by using a PLL, thelinearity of the reproduced waveform can be evaluated even in the casewhere the laser power deviates from the optimum laser power to cause amalfunction of the PLL.

Further, since the same recording pulse waveform is recorded for threetimes or more on a single track of the optical disk, and the reproducedwaveforms reproduced therefrom are averaged and used as a reproducedwaveform, the recording strategy can be optimized without an influenceby noise even in the case of a high recording density.

Further, upon optimizing the laser power by determining the pulseresponse so as to minimize the difference between the reproducedwaveform obtained by recording and reproducing the recording pulsesignal on the optical disk and the waveform obtained by the convolutionprocessing of the record data and the pulse response, since thedifference between the reproduced waveform and the waveform obtained bythe convolution processing of the record data and the pulse response isnormalized based on the information obtained from the reproducedwaveform, the laser power which provides a higher linearity of thewaveform and a signal amplitude as high as possible can be determinedwith accuracy.

Although the present invention is described based on the preferredembodiment thereof heretofore, the recording process and the recordingapparatus according to the present invention are not limited only to theabove embodiment, the recording process and the recording apparatusaltered without changing the gist of the present invention fall withinthe scope of the present invention. For example, the recording medium isnot limited only to the phase-change optical disk and any of the opticalrecording media such as magneto-optical disk and write-once optical diskmay be used as such. In addition, the 1-7 conversion used in thegeneration of the record data may be any conversion so long as itperforms RLL encoding such as a 2-7 conversion.

1. A method for adjusting a recording condition of optical information,comprising the steps of: irradiating an optical recording medium withlaser light having a recording pulse waveform generated based on arecording signal, which is in synchrony with clock cycles, to form arecord mark group on said optical recording medium; reading said recordmark group to obtain a reproduced waveform, and adjusting the recordingcondition by sampling said reproduced waveform at a period shorter thana clock period to evaluate a linearity of said reproduced waveform,wherein said adjusting step linearly interpolates sampled values of saidsampled reproduced waveform at a timing of R1 or R2 assuming a maximum,to extract times-series data of said reproduced waveform for respectiveclock cycles, given R1 and R2 being expressed by the following formula:$\begin{matrix}{{R1} = {( {n + 1} ) \times \frac{\sum\limits_{i}h_{i}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}\mspace{14mu}{and}}} \\{{R2} = \frac{\sum\limits_{k}y_{k}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}}\end{matrix}$ (i being an integer satisfying 0≦i≦m) respectively,wherein {a₀, a₁, . . . , a_(k), . . . , a_(n−1), a_(n)} represent saidtimes-series data for respective said clock cycles of the clock forrecording said optical recording medium, {y₀, y₁, . . . , y_(k), . . . ,y_(n−1), y_(n)} represent time-series data of said reproducing waveformfor respective said clock cycles (n being an integer not smaller thanzero, and k being an integer satisfying 0≦k≦n), and {h₀, h₁, . . . ,h_(m)} represent pulse responses of a recording/reproducing systemcorresponding to a specific recording/reproducing condition (m being aninteger satisfying 0≦m≦n).
 2. The method for adjusting the recordingcondition of optical information according to claim 1, wherein an indexof said linearity is obtained by the following formula:$ɛ = {\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - i} \times h_{i}}}} )^{2}}$(i being an integer satisfying 0≦i≦m), wherein {a₀, a₁, . . . , a_(k), .. . , a_(n−1), a_(n)} represent said times-series data for respectivesaid clock cycles of the clock for recording said optical recordingmedium, {y₀, y₁, . . . , y_(k), . . . , y_(n−1), y_(n)} representtime-series data of said reproducing waveform for respective said clockcycles (n being an integer not smaller than zero, and k being an integersatisfying 0≦k≦n), and {h₀, h₁, . . . , h_(m)} represent pulse responsesof a recording/reproducing system corresponding to a specificrecording/reproducing condition (m being an integer satisfying 15≦m≦n).3. A method for adjusting a recording condition of optical information,comprising the steps of: irradiating an optical recording medium withlaser light having a recording pulse waveform generated based on arecording signal, which is in synchrony with clock cycles, to form arecord mark group on said optical recording medium; reading said recordmark group to obtain a reproduced waveform, and adjusting a recordingcondition by evaluating a linearity of said reproduced waveform,characterized in that: said adjusting step is such that an index of thelinearity is obtained by the following formula:${R1} = {( {n + 1} ) \times \frac{\sum\limits_{i}h_{i}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}}$(i being an integer satisfying 0≦i≦m), wherein {a₀, a₁, . . . , a_(k), .. . , a_(n−1), a_(n)} represent said times-series data for respectivesaid clock cycles of the clock for recording said optical recordingmedium, [y₀, y₁, . . ., y_(k), . . . , y_(n−1), y_(n)] representtime-series data of said reproducing waveform for respective said clockcycles (n being an integer not smaller than zero, and k being an integersatisfying 0≦k≦n) and {h₀, h₁, . . . , h_(m)} represent pulse responsesof a recording/reproducing system corresponding to a specificrecording/reproducing condition (m being an integer satisfying 15≦m≦n).4. A method for adjusting a recording condition of optical information,comprising the steps of: irradiating an optical recording medium withlaser light having a recording pulse waveform generated based on arecording signal, which is in synchrony with clock cycles, to form arecord mark group on said optical recording medium; reading said recordmark group to obtain a reproduced waveform, and adjusting the recordingcondition by evaluating a linearity of said reproduced waveform,characterized in that: said adjusting step is such that an index of thelinearity is obtained by the following formula:${R2} = \frac{\sum\limits_{k}y_{k}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}$(i being an integer satisfying 0≦i≦m), wherein {a₀, a₁, . . . , a_(k), .. . , a_(n−1), a_(n)} represent said times-series data for respectivesaid clock cycles of the clock for recording on said optical recordingmedium, {y₀, y₁, . . . , y_(k), . . . , y_(n−1), y_(n)} representtime-series data of said reproducing waveform for respective said clockcycles (n being an integer not smaller than zero), and k being aninteger satisfying 0≦k≦n), and {h₀, h₁, . . . , h_(m)} represent pulseresponses of a recording/reproducing system corresponding to a specificrecording/reproducing condition (m being an integer satisfying 15≦m≦n).5. The method for adjusting the recording condition of opticalinformation according to claim 3 or 4, wherein said adjusting stepincludes the steps of sampling said reproduced waveform at a periodshorter than a clock period, and extracting time-series data of saidreproduced waveform for respective said clock cycles by linearlyinterpolating sampled values of said sampled reproduced waveform at atiming of said R1 or R2 assuming a maximum, given R1 and R2 beingexpressed by the following formula:${R1} = {( {n + 1} ) \times \frac{\sum\limits_{i}h_{i}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}\mspace{14mu}{and}}$${R2} = \frac{\sum\limits_{k}y_{k}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}$(i being an integer satisfying 0≦i≦m) respectively, wherein {a₀, a₁, . .. , a_(k), . . . , a_(n−1), a_(n)} represent said times-series data forrespective said clock cycles of the clock for recording said opticalrecording medium, {y₀, y₁, . . . , y_(k), . . . , y_(n−1), y_(n)}represent time-series data of said reproducing waveform for respectivesaid clock cycles (n being an integer not smaller than zero, and k beingan integer satisfying 0≦k≦n), and {h₀, h₁, . . . , h_(m)} representpulse responses of a recording/reproducing system corresponding to aspecific recording/reproducing condition (m being an integer satisfying0≦m≦n).
 6. The method for adjusting the recording condition of opticalinformation according to any one of claims 1, 2, 3, and 4, wherein saidoptical recording medium is a phase-change optical recording medium, andwherein, upon forming said record mark group on said phase-changeoptical recording medium by irradiating said phase-change opticalrecording medium with the laser light, an overwrite operation isconducted twice before obtaining said reproduced waveform.
 7. The methodfor adjusting the recording condition of optical information accordingto any one of claims 1, 2, 3, and 4, wherein three or more of saidrecord mark groups are recorded using recording pulse waveforms havingthe same form, said record mark groups are reproduced to sample three ormore reproduced waveforms, and samples values of said sampled reproducedwaveforms are averaged.
 8. The method for adjusting the recordingcondition of optical information according to any one of claims 1, 2, 3,and 4, wherein said record mark group is recorded by using a singlerecording pulse having a specific waveform, and said record mark groupis reproduced for three or more times to sample three or more reproducedwaveforms, and sampled values of said sampled reproduced waveforms areaveraged.
 9. The method for adjusting the recording condition of opticalinformation according to claim 7, wherein said three or more record markgroups are formed on a single track of said optical recording medium.10. The method for adjusting the recording condition of opticalinformation according to claim 3, wherein said R1 is adjusted so as tosatisfy 10×log R1>20-20(l/w) dB, given “w” being a beam diameter of thelaser beam used for recording/reproducing information, given “l” being ashortest mark length to be recorded on the optical-information recordingmedium.
 11. The method for adjusting the recording condition of opticalinformation according to claim 4, wherein said R2 is adjusted so as tosatisfy 10×log R2>21-20(l/w) dB, given “w” being a beam diameter of thelaser beam used for recording/reproducing information, given “l” being ashortest mark length to be recorded on the optical-information recordingmedium.
 12. The method for adjusting the recording condition of opticalinformation according to claim 2, 3, 4, 10 or 11, wherein said h_(i) hasa value determined using a least-squares method, and has a non-zerowidth larger than 15T, given T being a reference clock of data.
 13. Themethod for adjusting the recording condition of optical informationaccording to any one of claims 1, 2, 3, 4, 10, and 11, wherein, when thedata recorded on said optical information recording medium are expressedby “1” or “0”, a reference data is added before said recording signal asa reference timing for sampling said reproduced waveform, said referencedata having a duration of data “1” or data “0” different from the widthof said recording signal.
 14. A recording/reproducing apparatus foroptical information, comprising: an optical head irradiating an opticalrecording medium with laser light to receive reflected light therefrom;a laser drive for changing an optical intensity of an laser outputthereof; and a control section having the functions of: converting arecording signal, which is in synchrony with clock cycles, into arecording pulse waveform to transmit the same to said laser drive;sampling a reproduced waveform, reproduced from record marks on saidoptical recording medium, at a period shorter than a clock period;interpolating the sampled values; evaluating a difference between awaveform obtained by convolution of pulse responses determined from saidreproduced waveform and said recording signal and a waveform obtained bysampling said reproduced waveform and interpolating sampled valuesthereof at a timing of R1 or R2 assuming a maximum, to adjust a width orpower of said recording pulse waveform, given R1 and R2 being expressedby the following formula:${R1} = {( {n + 1} ) \times \frac{\sum\limits_{i}h_{i}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}\mspace{14mu}{and}}$${R2} = \frac{\sum\limits_{k}y_{k}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}$(i being an integer satisfying 0≦i≦m) respectively, wherein {a₀, a₁, . .. , a_(k), . . . , a_(n−1), a_(n)} represent said times-series data forrespective said clock cycles of the clock for recording said opticalrecording medium, {y₀, y₁, . . . , y_(k), y_(n−1), y_(n)} representtime-series data of said reproducing waveform for respective said clockcycles (n being an integer not smaller than zero, and k being an integersatisfying 0≦k≦n), and {h₀, h₁, . . . , h_(m)} represent pulse responsesof a recording/reproducing system corresponding to a specificrecording/reproducing condition (m being an integer satisfying 0≦m≦n).15. The recording/reproducing apparatus according to claim 14, whereinsaid evaluating is such that an index ε expressed by:${ɛ = {\sum\limits_{k}( {y_{k} - {\sum\limits_{i}{a_{k - i} \times h_{i}}}} )^{2}}};$is evaluated to adjust said recording condition, where 15≦m≦n.
 16. Therecording/reproducing apparatus according to claim 14 or 15, whereinsaid optical recording medium is a phase-change optical recordingmedium, and wherein, upon forming said record mark group on saidphase-change optical recording medium by irradiating said phase-changeoptical recording medium with the laser light, an overwrite operation isconducted twice or more before obtaining said reproduced waveform. 17.The recording/reproducing apparatus according to claim 13, wherein afunction of obtaining said reproduced signal includes the function ofaveraging three or more reproduced waveforms obtained by reproducing aplurality of record mark groups recorded by a plurality of recordingpulses having the same waveform, or the function of averaging thee ormore reproduced waveforms obtained by reproducing for a plurality oftimes a mark group recorded by a specified recording pulse waveform. 18.The recording/reproducing apparatus according to claim 15, wherein saidcontrol section controls said recording condition by defining thefollowing formula:${{{R1} = {( {n + 1} ) \times \frac{\sum\limits_{i}h_{i}^{2}}{\sum\limits_{i}( {y_{k} - {\sum\limits_{i}{a_{k - 1} \times h_{i}}}} )^{2}}}}\mspace{11mu},}\;$and said control section further has a function of determining arecording or erasing laser power so as to satisfy 10×log R1>20-20(l/w)dB, given w being a beam diameter of the laser beam, given l being ashortest mark length among said record mark group.
 19. Therecording/reproducing apparatus according to claim 15, wherein saidcontrol section controls said recording condition by defining thefollowing formula:${{R2} = {( {n + 1} ) \times \frac{\sum\limits_{k}y_{k}^{2}}{\sum\limits_{k}( {y_{k} - {\sum\limits_{k}{a_{k - 1} \times h_{i}}}} )^{2}}}},$and said control section further has a function of determining arecording or erasing laser power so as to satisfy 10×log R2>21-20(l/w)dB, given w being a beam diameter of the laser beam, given l being ashortest mark length among said record mark group.